To achieve a smooth power shift when more than one clutch is involved, the pressure versus time signature or profile curve for the clutches must be varied according to the torque transmitted by the transmission. Referenced in this regard Bulgrien U.S. Pat. No. 5,251,132, issued Oct. 5, 1993 to Ford New Holland, Inc., which discloses controlling clutch pressure based on output shaft speed. Essentially, according to that patent, one clutch is released, and pressure is adjusted in the corresponding on-coming clutch based on the rate at which the output speed drops. However, it has been found that controlling clutch pressure based on output shaft speed results in less than desirable levels of smoothness in shift. The output speed can also be allowed to drop too fast or too far for the control system to react and increase pressure in the on-coming clutch.
Thus, what is sought is a new method for measuring drive line torque for clutch control during power shifts which provides better reaction ability and smoother shifting.